Hydrogenation of secondary esters of omega-cyano carboxylic acids



United States Patent HYDROGENATION OF SECONDARY ESTERS OF w-CYANO CARBOXYLIC ACIDS Frederick Keith Duxbury and Owen Burchell Edgar, Manchester, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Sept.f30, 1957, Ser. No. 686,857

Claims priority, application Great Britain Oct. 3, 1956 6 Claims. (Cl. 260-482) This invention relates to new amino compounds, more particularly to esters of amino'acids, and to a process for the manufacture thereof.

It is known to reduce nitriles to primary amines by hydrogenation in the presence of catalysts, and to suppress the formation of secondary amines as by-products by carrying out the hydrogenation in the presence of ammonia. It is also known that esters react with ammonia, particularly when heated, to form amides. Attempts to reduce the ethyl esters of cyanovaleric acid in the presence of ammonia and a catalyst have resulted in only poor yields of the ethyl w-aminocaproate, since an appreciable proportion of the ester groups react with the ammonia or with the amino groups formed by the hydrogenation.

We have now found that, surprisingly, the secondary esters of amino acids may be readily obtained in good yield by hydrogenation of the secondary esters of cyanoacids.

Thus according to our invention we provide as new compounds the secondary esters of amino acids, of the formula:

wherein R stands for a hydrocarbon radical which may optionally bear substituents, and R stands for a. secondary hydrocarbon radical.

According to a further feature of our invention we also provide a process for the manufacture of the saidnew compounds which comprises hydrogenating a secondary ester of a cyano acid, of the following formula:

wherein R and R have the meaning stated above, in the presence of ammonia and a hydrogenation catalyst.

As esters of cyano acids which may be used in the process of our invention there may be mentioned in particular those esters of the stated formula wherein R stands for an aliphatic hydrocarbon radical, and wherein R stands for a secondary alkyl, or cycloalkyl radical. Thus there may be mentioned the iso-propyl, sec-butyl, sec-amyl and cyclohexyl esters of w-cyanobutyric acid, w-cyanovaleric acid, w-cyanocaproic acid, w-cyanooenanthic acid, w-cyanocaprylic acid and w-cyanopelargonic acid. There may also be mentioned the corresponding esters of aromatic cyano acids, for example m-cyanobenzoic acid.

It is preferred to use the isopropyl esters, since thereby there may be obtained the combined advantages of the present process, the accessibility and ease of preparation of the starting materials, and the comparative ease of distillation of the products.

The esters of the cyano acids may be made in known manner for example by reaction of esters of halogenoacids with metallic cyanides, by esterification of cyanoacids, or by the reaction of half-esters of dibasic acids with ammonia in the presence of a dehydrating catalyst as described in our co-pending application Serial No.

686,871, filed on even date herewith.

The hydrogenation catalyst to be used in the process.

pressure permitted for the vessel employed, preferably at.

150 to 250 atmospheres. The ammonia to be used is preferably anhydrous, and may be present in the proportion of 15% to and preferably 30%. to 50% by weight of the ester of the cyano acid employed.

Hydrogenation is usually complete in about 2 hours when a pressure of 200 atmospheres and a temperature of C. are employed.

[The amino ester may be isolated by any of the conventional methods, for example, by distillation to remove excess ammonia and other volatile by-products and then by distillation under reduced pressure. I

The amino esters are useful for chemical synthesis, and in particular for the manufacture of polymers. 7 These secondary esters are particularly useful since they are more stable than the primary esters, and also are obtainable by our process in better yield, for example the yield of isoproplyl aminocaproate by reduction of iso-propyl w-cyanoi A mixture of parts of iso-propyl w-cyanovalerate,.

40 parts of liquid ammonia and 20 parts of cobaltcatalyst are charged into an autoclave equipped with a stirring device. Hydrogen is forced into the vessel until the total pressure is approximately 170 atmospheres and the mixture is heated at a temperature between 110 C. and 130 C. Hydrogen is absorbed during a period of 1 to 2 hours, and then cases. The autoclave is then cooled, the contents are discharged and the catalyst removed by filtration. The product is isolated by fractional distill'ation of the filtered solution. 110 parts of iso-propyl waminocaproate, B.P. 110 C. at 17 mm. pressure together with 15 parts of residue are obtained. The yield of distilled iso-propyl- -aminocaproate corresponds to 83% of theory.

The cobalt catalyst comprises finely divided cobalt metal supported on kieselguhr.

Example 2 A mixture of parts of iso-propyl w-cyanovalerate, 40 parts of liquid ammonia, 15 parts of Raney nickel catalyst and 60 parts of iso-propanol is charged into an autoclave equipped with a stirring device. Hydrogen is forced into the vessel until the total pressure is approximately 120 atmospheres and the mixture is heated at a temperature of 80 C. Hydrogen is absorbed during a period of 1 t0 2 hours. The autoclave is then cooled, the contents are discharged and the catalyst removed by filtration. The product is isolated by fractional distillation of the filtered solution. 116 parts of iso-propyl w-aminocaproate, B.P. 74 C. at a pressure of 0.35 mm. of mercury, are obtained. The yield of distilled iso-propyl w-aminocaproatc corresponds to 76% of theory.

3 Example 3 A mixture of 202 parts of iso-propyl w-cyanocaproate, 52 parts of liquid ammonia and 20 parts of cobalt-onkieselguhr catalyst is charged into an autoclave equipped with a stirring device. The mixture is heated at a pressure of 240 atmospheres and a temperature of 120 C. for 2.5 hours and the product is isolated by fractional distillation as described in Example 1. 168 parts of iso-propyl waminoheptanoate, B.P. 120 C. at a pressure of 20 mm. of mercury, together with 23 parts of residue are obtained. The yield of distilled iso-propyl w-aminoheptanoate corresponds to 81% of theory.

Example 4 A mixture of 108 g. of sec-butyl w-cyanovalerate 31 parts of liquid ammonia and 12 parts of cobalt-on-kieseL guhr catalyst is charged into an autoclave equipped with a stirring device. The mixture is heated at a pressure of 240 atmospheres and a temperature of 120 C. for 2.5 hours and the product is isolated by fractional distillation as described in Example 1. 78 parts of sec-butyl w-aminocaproate, B.P. 122 C. at a pressure of 12 mm. of mercury, together with 17 parts of residue, are obtained. The yield of distilled sec-butyl w-aminocaproate corresponds to 71% of theory.

Example A mixture of 300 parts of iso-propyl w-cyanovalerate, 80 parts of liquid ammonia and parts of nickel-0nkieselguhr catalyst is charged into an autoclave equipped with a stirring device. The mixture is heated at a pressure of 120 atmospheres and a temperature of 80 C. for 2.5 hours, and the product is isolated by fractional distillation as described in Example 1. 240 parts of iso-propyl waminocaproate, B.P. 105 C. at a pressure of 13 mm. of mercury, together with parts of residue, are obtained. The yield of distilled iso-propyl w-arninocaproate corresponds to 78% of theory.

The nickel catalyst comprises finely divided nickel metal supported on kieselguhr.

Example 6 A mixture of 300 parts of iso-propyl w-cyanovalerate, parts of liquid ammonia and 15 parts of Raney nickel catalyst is charged into an autoclave equipped with a stirring device. The mixture is heated at a pressure of 120 atmospheres and a temperature of 100 C. for 2.5 hours and the product is isolated by fractional distillation as described in Example 1. 240 parts of iso-propyl w-aminocaproate, B.P. 116 C. at a pressure of 22 mm. of mercury are obtained. The yield of distilled isopropyl w-aminocaproate corresponds to 78% of theory.

Example 7 A mixture of 210 parts of. iso-propyl w-cyanovalerate and 11 parts of Raney nickel catalyst is charged into an autoclave equipped with a stirring device. The mixture is heated at a pressure of 100 atmospheres and a temperature of C. for 2.5 hours and the product is isolated by fractional distillation as described in Example 1. parts of iso-propyl w-aminocaproate, B.P. 70 C. at a pressure of 0.2 mm. of mercury are obtained. The yield of distilled iso-propyl w-aminocaproate corresponds to 42% of theory.

What we claim is:

1. Process for the manufacture of esters of amino acids which comprises subjecting to the action of hydrogen, a mixture consisting essentially of an ester of a cyano acid, of the following formula:

wherein n is an integer greater than 4 and R is selected from the group consisting of the isopropyl, secondary butyl, secondary amyl and cyclohexyl radicals, between about 15 and 75% ammonia, by weight of the ester, and a hydrogenation catalyst, under anhydrous conditions and at a temperature of between 25 C. and 200 C.

2. Process for the manufacture of the esters claimed in claim 1 wherein the hydrogenation is carried out at a temperature between C. and C.

3. Process for the manufacture of the esters claimed in claim 1 wherein the proportion of ammonia used is between 30% and 50% by weight of the ester of the cyano acid employed.

4. The process of claim 1 wherein the reaction mixture is distilled after said hydrogenation to recover the amino ester.

5. Process for the manufacture of the esters claimed in claim 1, wherein R stands for the iso-propyl radical.

6. Process for the manufacture of the esters claimed in claim 1 wherein the hydrogenation is carried out at a pressure of 150 to 250 atmospheres.

References Cited in the file of this patent UNITED STATES PATENTS 2,365,295 Schaaf Dec. 19, 1944 2,367,436 Ruggli et a1. Jan. 16, 1945 2,777,873 Hasek Jan. 15, 1957 OTHER REFERENCES Beilstein: vol. 4, 2nd ed., pages 782, 819, 871. 

1. PROCESS FOR THE MANAFACTURE OF ESTERS OF AMINO ACIDS WHICH COMPRISES SUBJECTING TO THE ACTION OF HYDROGEN, A MIXTURE CONSISTING ESSENTIALLY OF AN ESTER OF A CYANO ACID, OF THE FOLLOWING FORMULA: 